Coding Challenge Practice - Question 116

The task is to implement Promise.prototype.finally()

The boilerplate code

function myFinally(promise, onFinally) {
  // your code here
}

Promise.prototype.finally() could be used to return a callback when a promise is settled (fulfilled or rejected).

Attach .then to resolve the promise

return promise.then(

If the promise was fulfilled

(value) => {
return Promise.resolve(onFinally && onFinally()).then(() => value)
}

Promise.resolve is used because it converts normal value to a resolved promise.

If the promise is rejected

(error) => {
return Promise.resolve(onFinally && onFinally()).then(() => {
throw error
}

The final code

function myFinally(promise, onFinally) {
  // your code here
  return promise.then(
    (value) => {
      return Promise.resolve(onFinally && onFinally()).then(() => value);
    },
    (error) => {
      return Promise.resolve(onFinally && onFinally()).then(() => {
        throw error
      })
    }
  )
}

That's all folks!